Many of the processes by which a population of apparently similar blastomeres in the early embryo develops into a differentiated organism remain largely unexplored, despite the fact that developmental abnormalities are presumably traceable to defects in these processes. One such process is the disappearance of gap junctions with the onset of deteminative events, which might provide the isolation of cells necessary for differentiation. We have recently shown that intercellular communication among embryonic cells via gap junctions can be disrupted by a variety of agents, some of which (pH and voltage) may provide physiological regulation; we propose to examine whether known teratogens similarly affect intracellular communication. We have also developed optical techniques for detecting resting potentials and intracellular pH of cells within a developing embryo; we propose to follow changes in voltage and pH within single cells and cell groups while development progresses. Preliminary data suggest that regional differences in resting potential occur during gastrulation and that separate developmental compartments are distinguishable by this criterion alone. We propose to examine whether coupling occurs across compartmental boundaries and whether abolition of these boundaries disrupts development. Using pharmacological agents that selectively disrupt gap junctions, we hope to determine whether blockade at certain stages arrests development. This work will utilize embryos of fish, amphibia and mouse. The significance of this project is that it is directed toward understanding processes in early development that determine differentiation into a functional organism and whether abnormalities in development caused by chemical agents are attributable to the disruption of these processes.